ResolutionFirst, you need to choose a stable server that available from the Internet (DNS, SSH, Apache, etc.). It will be called "Probe host" or "Probe port" on the plugin configuration screen and will return a predefined string when you connect to it.
I choose SSH:
[user@host proxycheck-0.49a]$ telnet xxx.xxx.47.13 22 Trying xxx.xxx.47.13...
Connected to xxx.xxx.47.13.
Escape character is "^]".
So, to configure my test Parallels Business Automation - Standard (PBA-S) installation, I will use:
Probe host: xx.xxx.47.13
Probe port: 22
In your case, any STABLE internet service which returns a predefined value can be used (not only an SSH server).
1. Customer comes from src_ip.
2. After that, the proxycheck system scans some well-known ports of src_ip to find out where the proxy could run.
3. If proxies are found on src_ip, proxycheck tries to connect to our "Probe host" through the proxies found.
4. If the reply retrieved is exactly the same as we specified in "Reply," it means that the src_ip the customer comes from is an open proxy.
5. The corresponding customer's order will not be processed until it is approved by a provider.